Automatic telephone system



Feb. 10, 1925- 1,525,995

. E. JACOBSEN AUTOMATIC TELEPHONE sYsTEm Original Fi d Apri 15, 19155 5Sheets-Sheet l 5 v ITTOE/VEV Feb. 10, 1925. 1,525,995

' E. JACOBSEN AUTOMATIC TELEPHONE SYSTEM .1

Original Filed April 15, 191 8 3 Sheets-Sheet 2 Mi HM! Fbii. Z

iTTOE/VEV Feb. 10, 1925. I 1,525,995

' "E. JACOBSEN AUTOMATIC TELEPHONE SYSTEM Original ed April 15, 191 3Sheets-Sheet 5 //V//E/V TOE. fM/L J4coesE/v Patented Feb. lb, i925.

NITED STATES PATENT FFICFE.

EMIL JACOBSEN, 03 PORT WASHINGTON, NEW! YORK, ASSIGNOB TO AUTQMATICELEC- TRIC CCIEPANY, OE CHICfi-GO, ILLINOIS, A CGRPORATION OF ILLINOIS.

AUTQMAIIC TELEPHONE SYSTEli/I.

Application-filed April 1-5, 1918, Serial No. 228,545. Renewed March 16,1923 To all whom it may concern:

Be it known ;that I, EMI JAooBsEN,a citizen of the United gtates ofAmerica, and a resident of Port. Vashington, Nassau County, and State ofNew York, have invented certain new and useful Improvements inAutomatic-Telephone Systems, of which the following is a specification.

My inventionrelates in general to a telephone system in whichconnections are established by subscribers without the intervention ofan operator, by the use of automatic switches.

More specifically my invention relates to an improved method andapparatus-for. permit-ting a called subscriberin a brancheze change totransfer acall from his line tosome other line in the branch exchange.This invention is especially adapted to a system in which there are morethan one hundred subscribers in the branchexchange and in which bothselectors and connectors are used to find acalled line in said exchange.

Other systems havebeen invented by my-v self and others. which showmeans for extending or passing the call in a systemof one hundred linesor. less in which only connector switches are used, but this is thefirst time that such a scheme hasbeen applied to a larger system.Bypassing or transferring a call, I- mean the act of a. calledsubscriber, who, after beingcalled, may connect the party calling himwith any other subscriber without the necessity of anyoperation by the.calling line. This invention is especially useful in a system. whereasubscriber may seize a trunk line leading to a branch exchange andestablish a connection to a subscriber in the branch exchange thereover,now, instead ofthe calling subscriber having to hang up his receiver,CORP.

sult the directory, and then call again through all theswitches to asecond subscriber in the same branch exchange, he may simply inform thefirst called subscriber that he desires to speak with a certain othersubscriber, and the first called party may 'then operate certainvswitches, local to the branch exchange, to switch the connection to thesecond called party from the same trunk line which was seized by thecalling party. The second called party may in turn extend the call to athird subscriber and so on, so that any number of calls may be madewithout losing the trunk line vith which connection was firstestablished.

In order to accomplish this, I have provided a so-called dual orcompound selector switch, consisting of two selectors at the end of-anincoming trunk line of an exchange, which are used to extend connectionsfrom said trunk line through connector switches to called lines in thisexchange.

When a call is setup to this trunk line, one of saidselectors which maybe termed the main selector, is always operated by the digit of a callednumber to establish a connection to one of a number of connectorswitches in the usual manner, which connector is then operated toconnect with the called line. Now if, the called subscriber is not theparty desired or if another party is desired, the calling party mayinform this first called party of the number of the party desired sothat the called man ma then extend the call to this second callersubscriber. The back bridge relay of tin main selector is so arrangedthat when the first called subscriber now operates his dial to send thedigits of the second called subscribers number, this relay will controlthe operating magnets of the other selector (called the auxiliaryselector) to pick out another connector switch inthe branch exchange toconnect with the second called subscribers line. The second calledsubscriber may then extend the call again by operating the main selectorto find a third called party and so on. In this scheme it is onlynecessary for the called party to dial a three, digit number, while, ifsuch a scheme.

were not provided, the calling subscriber would have to release theentire connection,

which mighthave passed through any nu1nber of switches before reachingthe interexchange trunk line, and then dial perhaps five or six digitsto again connect with the inter-exchange trunk line to call anotherparty in the branch. In thevpresent case, 1 have arranged the circuitsso that the three parties (calling man and first and second called man)may stay in together if desired, while if the first called man hangs up,the selector and connector used to establish connection with his linewill be released. 1'

have also arranged the circuit so that a weak tone will be applied tothetalking c:r

cuit as long as three men stay in on a connection; so that, if twosubscribers desire to communicate secretly, a third subscribers presencein the connection will be known by them; and the tone is removed onlywhen one of the called men hangs up. This tone is so weak as not tointerfere with conversation, so that the three men may stay in and talkwithout any inconvenience from the tone.

In order to accomplish the desired results, I have taken certainfunctions usually performed by the connector switch and placed themunder control of the selector switch, the controlling relays being inthe selector in place of the connector.

Tar-ing described the general objects of my invention and the manner ofobtaining these results, I will now describe my invention by referringto the accompanying drawings in which my invention has been illustratedin connection with an automatic system of the latest type, in whichlocal and long distance connections may be established automatically.

' In Figure 1, l have. shown a. repeater E in the main exchange which isaccessible to a local subscriber or an operator in the main exchange andwhich is used in either case to repeat impulses over the two way trunkline extending to a branch exchange. This trunk line also terminates inthe main exchange in a line switch C which is operated over the trunkline to extend aconnection through the usual selectors and connectors toa called line in the. main exchange when the trunk line is seized by aselector at the branch exchange to call from branch to main. This trunkline also terminates in the main exchange in a. plurality of selectorrepeaters similar to that shown at D (Fig. 1) which are accessible to along distance operator preferably. The trunk line terminates in thebranch exchange in a pair of selectors (Fig. 2) which are connected inmultiple to the trunk line and may be termed the main selector F and theauxiliary selector G. The trunk line is also multipled into the banks ofoutgoing selectors in the branch exchange as shown.

The selectors F and G have access in common to a plurality of connectorswitches similar to that shown at H (Fig. 3), so that either selectormay seize any idle connector switch to call any subscriber in thisbranch exchange. I have shown a plurality of batteries throughout thedrawings, but it is to be understood that there is preferably but onebattery for each exchange.

I will first describe the operations when a subscriber in the. mainexchange seizes the repeater E and its associated trunk line to extend aconnection to a subscriber in the branch exchange.

When a call is extended to the repeater E a circuit is closed in theusual manner for the line relay 2 of said repeater over the two sides ofa calling line in series. Relay 2, upon energizing, closes a circuit forthe slow relay 3 to ground the release trunk and prepare a circuit forthe slow relay l. The ground which is connected to the release trunkmakes the repeater E busy at contact 5 and its multiples, causes thebridge cut-off relay 6 of the line switch C to be energized part way andalso makes the trunk line 7-8 busy at contact 9 in the bank of theselector repeater D and to others at its multiples.

The energization of relay 2 also closes a circuit at springs 10 which iscompleted a second later at springs 25 of relay 3 for the line relay ofthe main selector switch F (Fig. 2), said circuit extending from groundthrough the lower winding of line relay 12 of the selector F, lowerwinding of relay l3, springs 16 of relay 14, springs 17 and 18 of relay15, trunk conductor 8, springs 10, right hand winding of coil'19,springs 20 and 21, upper winding of relay 22, springs 23 and 24:,springs 25 of relay 3, trunk conductor 7 springs 26 and 27, springs 28,and upper windings of relays 13 and 12 to battery.

The line relay 12 energizes over the above traced circuit in the usualmanner to closea circuit at springs 29 and 30 for the release relay 31,which in turn ener izes to prepare a circuit for the vertical magnet andto ground the multipled release trunk 34: from ground through springs 32and 33 to the banks of outgoing selector switches. The relay 13 which isin series with the relay 12 is a differential relay and does notenergize in the above traced circuit.

Now when the calling device of the calling subscriber is operated toopen the line circuit a. number of times in accordance with a digit ofthe called number, the line relay 2 of repeater E will deenergize acorresponding number of times to repeat said impulses to the selectorswitch F over the inter-office trunk line 78. The slow relay l energizesand remains energized during the operation of relay 2 due to theintern'iittent ground applied to its circuit from ground through springs37 and 38. The relay 4, while energized, operates to short circuit thewindings of relay 22 and coil 19 to reduce the resist ance of therepeating circuit to the line relay 12. The circuit over which the relay12 receives impulses extends therefore from ground through the lowerwinding of said relay over the previously traced circuit to trunkconductor 8, through springs 10, springs 39 and 2%, springs 25, trunkconductor 7, and as previously traced through the upper winding of saidrelay to battery.

The relay 3 has previously closed a circuit for the electro-polarizedrelay 22 which has not energized up to this time as it requires bothwindings to be energized in the same directions before it Will attractits armas tures.

The line relay 12, upon each deenergizaion over the above circuit,operates to close a circuit for the slow relay and vertical magnet 36 inseries, from ground through springs 29 and 40, springs 42 and 41,springs 43 and 44, relay 35, and magnet 36 to battery. The magnet 36 isoperated to raise the wipers 4543 to some level of the banks in whichare located connectors, which have access to a desired group of lines.As soon as the Wipers leave their normal position the springs 49 and 50close Contact to prepare certain circuits. The relay 35, uponenergizing, closes a circuit from ground through springs 51 and 52,off-normal springs 50, re lay 53, off-normal springs 49, and releasemagnet 54 to battery. The magnet- 54 does not energize over this circuitdue to the higl'i resistance of relay Relay 53,-however, energizes tolock itself energized to ground through springs and 56 and to prepare acircuit for the rotary magnet 5?, As soon as relay falls back after theimpulses to the vertical magnet cease, the above prepared circuit forthe rotary magnet is completed from ground through springs 51 and 58,springs 59, and rotary magnet 57 to battery. The magnet 57 thereforeenergizes to step the Wipers 45%;8 onto the first set of contacts in theselected level and also opens the locking circuit of the interrupterrelay 53 at springs 56. Relay will immediately fall back and open therotary magnetcircuit at springs 59. Vhen the'magnet deenergizes at thistime a new circuit is prepared tor the interrupter relay 53 extendingfrom the test Wiper 48, through'springs 60 and 61. springs 56, springs50, relay 53, offnormal springs 49 and relay 54 to battery. Now if thefirst trunk line of this level, on the test contact of which the Wiper-48 now rests, is bus a ground will be present on said contact and relay53 will energize again over the above traced circuit from said ground toagain close the circuit of rotary magnet 57 at springs 59 and cause saidmagnet to rotate the Wipers to the next set of contacts Which are testedin the same manner. This alternate operation of relay and magnet 57continues until an idle trunk line leading to a connector H (Fig. 3) isfound, at which time there Will be no ground present on thecontacttested by Wiper 48 and relay 53 will not be again energized toclose the circuit of the rotary magnet. It will be noticed that duringthe rotation of the Wipers in search of an idletrunk line, the Wipercut-on relay 62 has been short circuited by the ground on successivebusy contacts through the Wiper 48, now however, when an idle trunk lineis reached, the relay 62 is no longer short circuited and will energizeoyer a circuit 8X tending from ground through the common low wound busyrelay .63, relay .62 and over the previously traced circuit throughrelay 53 and magnet 54 to batter. Relay is of comparatively highresistance andjdoes not permit any relay or magnet except itself toenergize over this circuit. Relay 62, upon energizing, over thiscircuit, prepares a circuit for the back bridge relay 64 at the springs65 and 66, prepares the ringing circuit at springs 67 and 68 connectsground through relay 63, through springs 69 and 60 and wiper 48 throughthe relay 70 of the connector H to battery, opens the circuit of thevertical magnet 36 at springs 43 and 44 and prepares a repeating circuitat springs 43 and 71 to the magnets of connector H. The ground throughrelay 63 to wiper- 4S acts as a guarding potential for the connector Hin the banks of other selectors such-as the selector Gr (Fig. 2) andmaintainsthe connector busy. The relay T0 of the connector H energizesover the aboye circuit including relay 63 to prepare a circuit atsprings 72 for the'operating magnets, opens the circuit of releasemagnet T6- at springs and 74 and prepares another circuit at. springs 73and 7 5 for the wiper cut-on relay to be described later.

The calli ng subscriber may now operate his calling device for-the next.digi t. of the called subscribers' inunber, thereby causing the linerelay 12 to again vibrate inresponse to the said impulses. The impulsesare in this case repeated by the line relay 12 to the magnet ofconnector H over the following circuit, ground through springs 29-and40, springs 41 and 42, springs 43 and 71, \yiper 47, springs 72,.springs77 and 78, relay 79', and verticalmagnet 80 to battery. This series ofimpulses causes relay T9 toremain energized during the transmissionthereof and operates-magnet 80 to stepthe wipers 83, 84 and 85 to adesired level of contacts in the bank. As soon as the wipers take theirinitial step at the first impulse, the of"- normal springs operate toclose a point in the circuit of release. magnet 76 at springs 82, openthe initial energizing circuit of relay 79 and magnet 80at springsT'Tand T3 and-close a new energizing circuit for said coils at springs77 and 81. The rest of the vertical impulses therefor pass through saidsprings 77 and 81, through the springs 86 and 87, closed by relay 79,through said relay 79 and magnet 80 to battery.

As soon as the impulses for this digit cease, the relay 79 deenergizesto prepare a circuit for the rotary magnet 88 and slow relay 39 atsprings 86 and 90. The relay 12, therefore, in response to the lastdigitot' the called number, operates to repeat said i1npulses over thepreviouslytraced circuit to springs 72, from thence through springs 77and 81, springs 86 and 90, relay 89, springs 91 and 92, and rotarymagnet 88 to battery. The operation of the magnet 88 causes the wipers83, 84 and 85 to be rotated onto the contacts which are connected to thedesired line leading in this case to the substation A. The relay 89remains energized, being slow acting, during this series of impulses, toshort circuit the springs 91 at springs 93, open the busy controlcircuit at springs 94, and closes a circuit for busy relay 96 at springs95. Relay 96 therefore energizes and remains energized for an instantafter the wipers come to rest on the desired line, to test the same. Ifthe called line be busy and a ground present at the test contact, thenrelay 96 will be locked energized by said ground through the wiper 85and springs 97 and 98 to battery through its upper winding. Relay 96,upon energizing, opens the circuit of the rotary magnet at springs 91,and closes the busy control circuit at springs 99. As soon now as relay89 falls back after the cessation of impulses to the rotary magnet, thebusy control circuit is completed at springs 94 and extends from batteryB through a resistance of approximately 200 ohms, through springs 99 and94, wiper 48, springs 60 and 69, and relay 63 to ground. The relay 63receives enough current to attract its armature in this case andoperates to connect busy signaling cur-- rent from busy machine Mthrough springs 100 to the trunk conductor 8 and thence to the callingsubscriber. The calling subscriber upon hearing this busy tone may thenhang up his receiver and release the connection in the usual manner.

Assuming now that the substation A were idle when called, then whenrelay 96 of connector H energizes after connection is made with saidline it will have no locking circuit closed for its upper winding and assoon as relay 89 falls back after impulses cease and opens springs 95,relay 96 will deenergize and prepare a circuit for the wiper cut-onrelay 101, extending from ground through the upper winding of saidrelay, springs 102 and 97, test wiper 85, bridge cut-off relay 103 ofthe line switch C, and magnet 104 to battery. Relays 101 and 103 onlyenergize over this circuit, relay 103 attracting its armatures only farenough to disconnect ground and the operating magnets of switch C fromthe called line, without connecting said line to the wipers. Relay 101,upon energizing, opens the circuit of the rotary magnet at springs 92,closes a locking circuit for its own lower windin at springs 105,connects ground direct to wiper 85 through springs 106, and connects thecalled line conductors through to the ringing circuit at springs 107 and108 to signal the called station. The circuit for ringing the calledstation instead of being from the connector as is usual to automaticsystems extends from the selector over the following path, from batterythrough the upper winding of relay 109, through springs 111 and 110,springs 67, wiper 45, springs 107 wiper 83, to and through the ringingequipment of substation A, and back through wiper 84, springs 108, wiper46, springs 68, springs 112 and 113, to the armature of the interrupterrelay 114, which relay operates to connect said circuit first to thegenerator R and then to the booster battery B The called subscriber uponhearing his call signal removes his receiver in response thereto andcloses a direct current circuit for the relay 109 through the receiverhook springs. The relay 109 will immediately energize over this circuitand disconnect the ringing circuit from the called line at springs 112and 113, and 110 and 111. Further results of the energization of relay109 are as follows; the talking circuit from the called line isconnected to the windings of the back bridge relay 64 through springs110 and 115, and springs 112 and 116; the closure of springs 117 and 118closes a locking circuit for the lower winding of relay 109, extendingfrom ground through springs 121 of relay 13, springs 117 and 118,springs 66, and the lower winding of said relay 109 to battery; thisground is also connected to one end of the lower winding of back bridgerelay 64. The relay 64 is now energized over a circuit extending fromground through springs 121, springs 117 and 118, lower winding of relay64, springs 116 and 112, springs 68, wiper 46, springs 108, wiper 84,through the talking equipment of substation A, and back over the otherside of the line through wiper 83, springs 107, wiper 45, springs 67,springs 110 and 115, springs 65, and upper winding of relay 64 tobattery. This relay therefore supplies talking battery to the calledsubscriber and also energizes to close a circuit at springs 122 and 123for the slow acting relay 124, and to close one point in a signalingcircuit at springs 125. The relay 124 energizes to prepare a circuit forthe operating magnets of the auxiliary selector G at springs 126 and12'. and also closes a circuit at springs 128 from ground through saidsprings through relay 15 to battery. Relay 15 will therefore energize toreverse the connections of the line relay 12 with regard tothe trunkconductors 7 and 8, thereby reversing the flow of current flowing oversaid trunk conductors to the Winding of the relay 22 of the repeater E.Relay 22, being an electropolarized relay as before pointed out, willnow energize with the following results: The springs 129 close contactto short circuit the impulsing springs 10 of the line relay, the springs131 close contact to short circuit the springs 23 and Y24, and springs130 close contact ,to energize the reversing relay 132, which in turnenergizes to reverse the flow of battery in the calling line for anydesired purpose and to open th'e'con} tact of springs 20 and 21 andclose contact of springs 2l'and 133. The holding circuit of the linerelay. 12 through the repeater now extends from the trunk conductor 8through springs 129; both windings of coil 19 in series, upper windingof relay 22, springs 131, and springs 25 to thetrunl'c' conduc tor 7.The calling and called subscribers may now converse over the heavyconductors. shown extending through repeater E, selector l3, andconnnector H.

lVhen conversation is completed the connection may be released by thehanging up of the receiver at the calling station. Relay 2 of repeater Ewill theretoredeenergize and through the medium of relay 3 will open theholding circuit fol-the line relay 12 of selector F in the usual manner.Relay 12 in turn de'energizes to open the circuitof slow relay 31, whichin turn Cleenergizes to remove ground from the release trunk and close acircuit for the release magnet 54 at the back contact of spring 42. Thisswitch F will. therefore immediately release and open the circuit, ofthe holding relay of the connector l-l. Relay 70, upon deenergizing,closes a point at.

springs 73 and 74, in the circuitof the release magnet T6,therebycausing the re-. lease of the connector and thus the entire connectionis released.

Let us assume now that the calling subscriber, who has directed theextension of, the previously described connection, desires to talk withsome other subscriber in the same branch exchange with the subscriber A.In the old practice the calling subscriber. would be obliged to releasethe entire connection and again go through the entire process of seizinga repeater E and another trunk line similar to 78, and so on, and in thecase of a busy branch exchange the inter-othce trunk lines might be sobusy that he would have to wait sometime before his second call could becompleted. In my improved system, as explained, I have an ranged thecircuits so that the calling subscriber need not release the entireconnection, but need only inform the called subscriber of the otherparty to whom he desires to converse and the called pa rty inay thenextend this connection to said desired party by operating the auxiliaryselector G' and some other connector switch similar to H. to find thedesired called line, that is only three digits will be required for suchextension of the connection.

I will now describe the operations which are performed by the, calledsubscriber at substation A when the calling subscriber, before releasingthe abovedescribed which:

which theline relay 2 ot the repeater was operated by the callingsubscriber. Eachtime-the relay 64 falls back it closes a circuit for thevertical magnet ot the auxiliary selector which was previously, preparedby the slow,relay,'124 this circuit extends from ground through springs122 and 134, springs 126 and 127, springs135 and 136,slow relay 137.,and vertical mag-- net 138 to battery. The vertical magnet 138 operatesin the usual manner to raise the wipers 139 140, 141 and 142 to somelevel of the bank in which connectorsare located having access to thegroup of, lines in Which the called subscriber is located; As soon assaid wipers, leave normal position, the ofl normal springs 143 and 144are operatedto prepare certain circuits. The re,- lay 137 holds inenergized position during the operation of magnet 138 and in thisposition, closes a circuit at springs 145 and 146 extending throughsprings 144, relay 147,-

springs 143, and magnet 148 to battery; Only the relay 147 energizesover this circuit and said relay 147 prepares a circuit for therotarymagnet 149 at springs 150, and closes a locking circuit for itself atsprings 151 extending through the springs v 152 of the rotary magnet.After the vertical impulses cease, the circuit of relay 137 is opened bythe relay 64 said relay.,137 therefore deenergizesafter an instantandcompletes the circuit for the rotary magnet 149 from ground throughthe springs 145 and .153, and the springs 150. The rotary magnet 149will therefore energize immediately to step the wipers 139142 inclusiveonto the first set of contacts of the selected level and also opens theholding circuitof relay 147 at springs 152. Relay 147 will thereforedeenergize and in turn' open um neuit of the rotary magnet at springs150. Now if the connector associated with the first setofcontactsisfbusy, then as soon.

' as" relay i149 falls; bacltt he circuit of magnet 14? will. ag in beclosed from ground through Wiper 141;, springs 154 and 155, springs'152springs 144, and relay 147 to battery through the release magnet The re-I lay 14 will. again energizetherefore to again close the circuit of therotary magnet at springs 1'50 and step the wipers to the 11631 set ofattract-etc be tested, This alternate operation of the relay 147 andmagnet 1.49 continues until an idle trunk is found and the Wiper 141finds an ungrounded contact thereof, at which time no circuit will beclosed for relay 147. The relay 156 has been held short circuited duringthe rotation of the switch over busy contacts and will now be energizedwhen said short circuit is discontinued, the circuit for energizingrelay 156 extending from ground through relay 63, winding of relay 156,springs 152, and relay 147 and magnet 148 to battery. Re lay 156 is ofsuch high resistance that it alone will energize over this circuit, andupon energizing, closes a pair of springs 157 in the circuit of thebackbridge relay 158, extends the impulsing circuit from the springs ofrelay 64 to the magnets of the connector seized, through springs 135 and159, closes a pair of springs 160 and 161 in the talking circuit toprepare for signaling, and closes the springs 154 and 162 in contact.For the purpose of this explanation the connection will be described ashaving been extended to the connector H (Fig. 3) although it will beunderstood that the selector G will, of course, select some otherconnector similar to H, as H is already busy. Now when the springs 154and 162 of relay 156 are closed, a circuit is thereby closed for therelay of the connector H (Fig. in the same manner as by the relay 62 ofthe selector F. The magnet of the connector will now be operated over acircuit extending from ground through springs 122 and 134, springs 126and 127, springs 135 and 159, wiper 142, springs 72, springs 77 and 78,and relay 79 and magnet 80 to battery. The connector seized Will beoperated in the same manner as explained for the connector H when seizedby the selector F to find and test the second called line, except thatthe control circuit passes to the backbridge relay 64 of the mainselector instead of to the line relay 12 of said selector. As soon asthe desired line is located, the connector will test for busy in themanner hcreinbetore explained and if busy, then relay 96 closes thesprings 99 to connect battery B through the resistance to operate relay63 over the circuit including the wiper 141 of selector G.

Assuming the second called line to be idle, then as soon as the relay101 energizes and closes the springs 107 and 108, a ringing circuit willbe closed to the said second called station extending from batterythrough the upper winding of the ring cutoil relay 163, through springs164 and 165, springs 160, wiper 139, springs 107, wiper 83, to andthrough the ringer of the second called station, wiper 84, springs 108,wiper 140, springs 161, springs 166 and 167, to the armature of theinterrupter relay 114. The relay 114 operates to alternately connect theabove ringing circuit to booster battery B and generator R- in the usualmanner so that the instant the called subscriber responds to said signalthe relay 163 will be energized to disconnect said ringing circuit. Therelay 163, upon energizing, connects ground from springs 121 of relay 13ot selector F through springs 168 and 169 to one end of the lowerwinding of the back bridge relay 158 and through springs 168 and 169 andthe springs 170 to the lower winding of relay 163, to lock said relay163 energized. The closure of springs 166 and 171 and 165 and 172connects the windings of the back bridge relay 158 across the calledline. The relay 158 will therefore energize over the following path,ground through springs 168 and 169, lower winding of relay 158, springs171 and 166, springs 161, wiper 140, springs 10 8, wi )er 84, calledsubstation, wiper 83, springs 10, wiper 139, springs 160, springs 165and 172, springs 157, and upper winding of relay 158 to battery. Therelay 158, upon energizing over this circuit, operates to close acircuit at springs 173 and 174 for the slow release relay 175. Relay 175energizes to supply an additional ground to the winding of the reversingrelay 15 through springs 176 and to prepare another circuit at springs177 and 178. A further result of the energization of relay 158 is toclose another point at springs 17 9 in a signaling circuit whichindicates to the subscribers, both calling and called, that threeparties are now across the line, and in case the calling party desiressecret communication with either the first or second called parties shemay wait until this tone leaves the connection. This tone is connectedin a chain arrangement from the tone generating device M throughcontacts 125 of the back bridge relay 64 of the selector F throughsprings 17 9 of the back bridge relay 158 of selector G and thence to aconductor of the talking circuit, so that it will be disconnected assoon as either of the called parties hang up. It will be understood thatthis tone generated by the ma chine M is very low and does not interferewith conversation, so that the three parties may stay in on theconnection if desired. The calling party may now talk to the secondcalled subscriber over the heavy conductors shown extending from thetrunk line 7-8 through the selector G and the connector H, or itsduplicate.

It at this time the first called subscriber desires to withdraw from theconnection, he may do so by simply restoring his receiver and leave thecalling subscriber connected for conversation to the second calledsubscriber only. YVhen the receiver at the first called station isrestored, the circuit of the back bridge relay 64 ot the selector F(Fig. 2) is opened in the usual manner. As relay 64 deenergizes acircuit is closed extending from ground through springs 122 and 134,

springs 126 and 180, springs 118, springs 181 and 182, oH-normal springs49,, and release magnet 54 to battery. The magnet 54 will thereforeenergize to release the main selector F and the connector H to normal inthe manner explained, whereby the second called subscriber only is heldin across the conductors 7 and 8.

After conversation has been completed with the second called subscriber,this connection may be released by the restoration of the receiver atthe callingstation. In this case the relay 12 will be deenergized in theusual manner to open the circuit of the release relay 31. Relay 31, upondeenergizing, closes a circuit from ground through springs 23 and 183,off-normal springs 1-13 of selector G and release ma net 148 to bate.

tery. The magnet 1 18 will release the switch G to normal in the usualmanner and also cause the release of the selected connector switch fromthe called line.

Should the calling subscriber have desired to only talk with the second.called subscriber for a short interval .andthen again continue hisconversation with the first called man, then the second calledsubscriber would be told to hang up as soon as desired. .Vhen the secondcalled subscriber restores his receiver to the hookwh le the firstcalled man is still in on the connection,

then only the selector G and its associated connector switch will bereleased and the calling man will be left connected to the.

lVhendisconnected and restored the main selector switch to normal. Nowif, after conversing with. the second called subscribertor a time, thecalling subscriber desires to be connected to still another or thirdcalled subscriber, she will make a request for such connection to thesecond called man. The second called man may then operate his callingdevice to control the magnets of the main selector through the medium ofrelays 158 and 175 in the same manner in which the magnets of theselector G were controlled by the first called subscriber through themedium of the relay 64. i

It will be seen therefore that this transferring or extension of thecall may be carried on indefinitely and that the calling subscriber mayhold the trunk line 78 as long as desired and may be connected over saidtrunk line to as many as desired of the subscribers in the branchexchange successively or any two at once. Also. that'this scheme isarranged so that the connectors are veryslmple of construction andthatmany of the tion, it being shownonly to show more fully the adaptabilityof the dual selector arrangement such as employed at F and G, to asystemin which long distance apparatus is used.

l Vhen the-toll operator plugs into the jack of selector repeater D, anoperating circu't is closed at springs 186 for the line relay-187. Relay187 closes a circuit for release relayv 188 at. springs 189 and 190.Relay 188 prepares a. circuit for the vertical magnet and connectsground to the supervisory lamp through springs 191. Relay 187 will nowbe operated to control the circuit of slow relay I 192 and verticalmagnet 193 in the usual manner to raise the wipers to a des red level.

Relay 192 during this operation energizes.

relay 19 1 which in turn prepares a circuit for rotary magnet 195, whenrelay 192 falls back the circuit of rotary magnet 195 is completed andsaid magnet is then controlled by relay 194 to step the wipers on to anidle trunk line in the usual manner. hen such idle trunk l'nc isreached, the relay 196 will immediately energize to connect ground tothe private wiper, lock itself energized, and switch the impulsingcircuit from slow relay 192 and magnet 193 to the slow relay 197.

N ow when the next series of impulses are delivered to relay 187, saidrelay operates to maintain relay 197 energized, and to close a repeat ngcircuit to the trunk line 78 and thence to the line relay 12 of the mainselector F at the springs 198. Inthis manner the impulses are repeatedto the main selector to .causeit to pick out an idle connector H in themanner before pointed out and to cause said connector to seize a desired called line. No when such connection is completed and the relay 15of the trunk line is operated to reverse the flow of battery in thetrunk line, such reversal causes the electropolarized relay 199 tocperate to close the series circuit of the repeating coil at springs 200and to include the relay 201 in series with the relay 187 in theoperating circuit. Relay 201 now remains energized and relay 187 fallsback, so hat the release magnet may now be con trolled by relay 201.Should the called sub "cut-off relay 109 or the relay 163'.

scrlber hang up too soon or the operator dcsire to rering the same, shewill then opcrate the tuned relay 292 to ground one side of the trunkcircuit extending to the selector F. This grounding of one side of thetrunk causes the dilferent-ial relay 13 of said selector F to energizeand open, at the springs 121, the locking circuit for either the ringThis causes either or both of said ring cutoff relays to deenergize toagain start the automatic ringing in the usual manner. After theselector F at the branch exchange has been operated from the selectorrepeater D, it will be understood that the same extending ortransferring operations may be car ried out as when the selector wascalled from the straight repeater E.

As explained at one point in the description, the trunk line 78 is a twoway trunk, that is, calls may be set up in either direction thereover.For this purpose the trunk line '78 is multiplied into'the banks ofoutgoing selectors of the usual type in the branch exchange by means ofconductors such as 203, 204C, and 34. When a selector is operated toseize said conductors, a ground will be connected to conductor 34 to0perate the cut-off relay 14. Relay 14. upon energizing, operates todisconnect the trunk line 7-8 from all connection with the selectors Fand G. The connection may then be extended from the main exchange end ofthe trunk line by means of the rotary line switch C in a well knownmanner.

It will be seen therefore that I have provided a Very simple andeflicient method of extending or transferring calls in large automaticsystem and that said result is accomplished in a highly improved mannenHaving fully described and ascertained the features and operation of myinvention,

what I consider to he new'and desire to have protected by Letters Patentwill be pointed out in the appended claims.

What I claim as my inventionis:

1. In a telephone system, a trunk line. a pair of automatic switchesassociated with said trunk line, other automatic switches accessible tosaid pair of switches, means for seizing said trunk line, and foroperating one of said pairof switches to seize one of said secondswitches, and for operating the seized second switch to extend aconnection to a calledline,connections whereby the other of said pair ofswitches may be operated over the connected called line. to establishconnection. with a second called line, and a signal for indicating tothe subscribers when the connection includes more than one calledsubscriber.

2. In a telephone system, main and auxiliary selector switches connectedin pairs, connector switches accessible in common to said selectorswitches, means whereby a calling subscriber may operate one of saidmain selectors to extend a connection to a called line through one ofsaid connector switches, means whereby the subscriber on the called linemay operate the associated auxiliary selector to transfer the call to asecond called line through a second one of said connector switches, anda signal for indicating to the subscribers when the connection includesmore than one called subscriber.

3. In a telephone system. automatic selector switc hes. connectorswitches accessible thereto, means controlled by'a calling subscriberfor seizing a selector switch and for operating it to select one of saidconnector switches and for then operating said connector switch to finda called line and extend a connection thereto. together with meanscontrolled from the called line over said extended connection foroperating another selector switch and another connector switch to extendthe connection to a second called subscriber while maintaining theconnection betweenthe calling party and the first called line.

4. In a telephone system, a trunk line, main and auxiliary selectorsassociated with said trunk line, a connector accessible to saidselectors in common, means for operating either of said selectors toseize said connector to extend a connection to a called line, means formaking the called line busy,

a relay common to said selectors, and means in said connector responsiveto the busy condition of said line for operating said common relay toconnect a busy tone to the said extended connection.

5. In a telephone system, a pair of automatic. switches. other switchesaccessible thereto, means controlled by a calling subscriber for seizingsaid switches. means for operating said switches alternately from calledlines to extend connections to other called lines, through saideotherswitches, a release magnet for'each switch, means controlled by thecalling subscriber for operating the release magnet of each switch, andmeans controlled over any connected called line for operating therelease magnet of the associated switch only when the other of saidswitches is in connection with another called line. 1

6. In a telephone system, main. and auxiliary selector switchesconnected in pairs, connector switches accessible in common to saidselector switches, means whereby a calli said connector switches whilemaintaining.

the original connection intact, thereby establishing a three partytalking c1rcu1t,and release mechanism in the main selector controlled bythe subscriber on the first called line.

8. In a telephone system, main and auxiliary selector switchesconnect-ed in'pairs, connector switches accessible in common to saidselector switches, means whereby a calling subscriber may operate one ofsaid main selectors to extend a connection to a called line through oneof said connector switches, means whereby the subscriber on the calledline may operate the associated auxiliary selector to extend the call toa second called line through a second one of said connector switcheswhile maintaining the original connection intact, thereby establishing athree party talking circuit,'release mechanism in the main selectorresponsive to the replacement of the receiver at the station on thefirst called line, circuit arrangements such that the subscriber on thesecond called line can reoperate the main selector and a connector toextend the call to a third line, and release mechanism in the auxiliaryselector controlled by the subscriber on the second called line.

9. In a passing call system, a pair of switches, a line and a releaserelay in each switch controllable by a called subscriber to pass a call,a release magnet, in each switch, a ring-cut-ofi" relay in each switch,and a circuit for each release magnet con trolled by the release relayof the same switch and the rin -cut-ofi relay or" the other switch.

10. In a passing call system, a pair of switches, a line and a releaserelay in each switch controllable by a called subscriber to pass a call,arelease magnet in each switch, a ring-cut-off relay in each switch, anda circuit for each release magnet controlled by the release relay of thesame switch and by the ringcut-ofi relays in both switches.

11. In a passing call system, a pair of switches, operating means insaid switches under the control of call-ed subscribers to pass calls, arelease magnet in each switch,

two circuits each having two branches 8X? tending to the release magnetsof said switches, respectively, a release relayin one of said switchescontrolled ,by it called Subscriber for closing one of said circuits atthe undivided end thereof, and a similarrelease relay in the otherswitchior closingthe other circuit at the undivided end thereof.

12. In a passing call system, a pair of switches, operating means insaid switches under the control of called subscribers to pass calls, arelease magnet in each switch, two circuits each haying two branchesextending to the release magnets ot said switches, respectively,arelease relay in one of said switches controlled by a called subscriberfor closing one of said circuits at the undivided end thereof, a similarrelease relay in the other switch for closing the other circuit at theundividedend thereof, athird relay in one switch under called subscribercontrol to shift the branches of one pair separately into connectionwith the associated main circuit, and a fourth relay in the other switchunder called subscriber control to shift the branches of the other pairseparately into connection with the associated main circuit.

13. In a telephone system, automatic switching mechanism for extending aconnection from a calling line to a called line, means includingauxiliary switching equipment controlled by the subscriber on theconnected call-ed line for extending the connection to a second calledline while, maintaining the first connection, a signalling machine, andmeans for automatically connecting said machine to the calling line whenthe subscriber on the second called lineanswers the call.

14. In a telephone system, automatic switching mechanism for extending aconnection from a calling line to a called line, means includingauxiliary switching equipment controlled by the subscriber on theconnected called line for extending the connection to a second calledline whilemaintaining the first connection, a signalling machine, meanstor automatically connecting said machine to the calling line when thesubscriber on the second called line answers the call, and means forautomatically disconnecting said machine from the calling lineresponsive to the replacement of the receiver at the station on thefirst called line. 15. In a telephone system, automatic switchingmechanism for ext-ending a connection from a calling line to a calledline, means including auxiliary switching equipment controlled by thesubscriber on the connected called line for extending the connection toa second called line while main taining the first connection, andsignalling means for placing a faint tone on the talle ing connection sothat each of the three connected subscribers will know that two othersare involved in the connection.

16. In a telephone system, automatic switching mechanism for extending acon nection from a calling line to a called line,

7 means including auxiliary switching equipment controlled by thesubscriber on the connected called line for extending the connection toa second called line while maintaining the first connection, means controlled by the subscriber on the second called line for extending theconnection to a third called line in case the subscriber on the firstcalled line hangs up, and signalling means for notifying the callingsubscriber whenever two called lines are connected for conversation atthe same time.

17. In a telephone system, an operators switchboard, means including aplurality of selector switches and a final connector for extending aconnection from said switchboard to a called line, an auxiliary selectorpaired with one of said first mentioned selectors, means under thecontrol of the subscriber on the connected called line for operatingsaid auxiliary selector and another connector to extend. the establishedconnection to a second called line, signalling means associated withsaid paired selectors, a ring-cut-ofi relay in each of said pairedselectors for disconnecting the signalling means when the subscriber ona connected called line answers, a locking circuit for each relay, andmeans controlled by the operator at said switchboard for opening saidlocking circuits without releasing any connection which may beestablished.

18. In a telephone system, an operators switchboard, means including aplurality of selector switches and a final connector for extending aconnection from said switchboard to acalled line, an auxiliary selectorpaired with one of said first mentioned selectors, means under thecontrol of the subscriber on the connected called line for operatingsaid auxiliary selector and another connector to extend the establishedconnection to a second called line, signalling means associated withsaid paired selectors, a ring-cut-ofl relay in each of said pairedselectors for disconnecting the signalling means when the subscriber ona connected called line answers, circuits for locking eitherring-cut-ofi relay when operated to prevent its deenergization when thecalled party hangs up, and means controlled by the operator at saidswitchboard for openin the locking circuit of either ring-cut-ofi relaywhen the same is locked in order to rering the called subscriber.

19. In a telephone system, an operators switchboard, means including aplurality of selector switches and a final connector for extending aconnection from said switchboard to a called line, an auxiliary selectorpaired with one of said first mentioned selectors, means under thecontrol of the sub scriber on the connected called line for operatingsaid auxiliary selector and another connector to extend the establishedconnection to a second called line, signalling means associated withsaid paired selectors, a ring-cut-oll relay in each of said pairedselectors for disconnecting the signalling means when the subscriber ona connected called line answers, circuits for locking eitherring-cut-ofi relay when operated to prevent its deenergization when thecalled party hangs up, means controlled by the operator at saidswitchboard for opening the locking circuit of either ring-cut-otf relaywhen the same is locked in order to rering the called subscriber, saidunlocking means comprising a differential relay in series with thecontrolling line relay of one of said paired selectors, and anotherrelay responsive to ringing current from said switchboard for groundingone conductor of the talking circuit to operate said differential relay.

Signed by me at Chicago, Cook County, State of Illinois, this 11th dayor" April, 1918.

EMIL JACOBSEN.

